Thanks. I tried again before going to bed last night and just left it running - in the morning it seems to have completed OK, just took a mighty long time with no initial indication of any progress. Still don't understand why first cut (similar size) was so much quicker...

I downloaded Bandicut because I want to cut a long (5 1/2 hour) MP4 film into 4 shorter chapters. A cut from the middle of the film progressed quickly and successfully. But a similar length section at the end of the film has been using almost all my CPU for 2 1/2 hours and progress still sitting at ...